In general, a foldable cellular telephone includes, as shown in FIGS. 18 and 19, a transmission section A and a reception section B. The transmission section A and the reception section B are turnably connected through a hinge assembly (not shown) for turning between a non-talk position where the transmission section A and the reception section B are abutted with each other as indicated by a solid line of FIG. 18 and a talk position as indicated by a solid line of FIG. 19. Moreover, when the angle formed between the transmission section A and the reception section B is smaller than α, the transmission section A and the reception section B are turned into a non-talk position by bias means built in the hinge assembly and held in that position. When the angle formed between the transmission section A and the reception section B is brought to be larger than a predetermined angle β, the transmission section A and the reception section B are turned into the talk position by bias means and held in that position.
As shown in FIG. 20, the hinge assembly includes a pair of abutment plates (abutment members) C,D arranged in mutually opposing relation and bias means (not shown) for biasing the paired abutment plates C,D towards each other. The pair abutment plates C,D are non-turnably connected to the transmission section A and the reception section B, respectively. Therefore, the abutment plates C,D are relatively turned as the transmission section A and the reception section B are turned.
The abutment plate C has a pair of projections C1, C1 which are formed on its opposing surface with respect to the abutment plate D and which are arranged 180 degrees away from each other in the circumferential direction. The remaining abutment plate D also has a pair of recesses D1, D1, which are formed on its opposing surface with respect to the abutment plate C and which are arranged 180 degrees away from each other in the circumferential direction. The projection C1 and the recess D1 retain the transmission section A and the reception section B in a non-talk position or in a talk position with the help of the biasing force of the bias means.
Specifically, as shown in FIG. 21, the projection C1 and the recess D1 are arcuate in section. When the transmission section A and the reception section B are in the non-talk position, the projection C1 and the recess D1 are, as shown in FIG. 21(A), abutted with each other at areas which are slightly circumferentially away from their centers. Owing to this arrangement, the biasing force of the bias means is converted into a rotational biasing force (rotation biasing force for turning the abutment plate D in a direction opposite to the arrowed direction) for turning the abutment plate C in the arrowed direction. By this rotational biasing force, the transmission section A and the reception section B are held in the non-talk position. As shown in FIG. 21(B), when the angle formed between the transmission section A and the reception section B is β or less, an area which is slightly away from the central part of the projection C1 contact one end portion of the recess D1. By this, the abutment plate C is biased in the arrowed direction of FIG. 21(B) and the transmission section A an the reception section B are turned in the non-talk position. When the angle formed between the transmission section A and the reception section B is β or more, the projection C1 and the recess D1 are brought into a symmetrical state with respect to the state shown in FIG. 21(B). Accordingly, the abutment plate C is biased in a direction opposite to the arrowed direction and the transmission section A and the reception section B are turned as far as to the talk position. When the transmission section A and the reception section B are located in the talk position, the projection C1 and the recess D1 are press-contacted at their central areas with each other as shown in FIG. 21(C). In that connection, the biasing force of the bias means merely urges the projection C1 against the bottom surface of the recess D1 and is never converted into a rotational biasing force. However, when the abutment members C,D are turned into either one direction from the position (hereinafter referred to as the “neutral position”) shown in FIG. 21(C), the biasing force of the bias means is converted into a rotational biasing force and causes the abutment members C,D to return into the neutral position. Accordingly, the transmission section A and the reception section B are held in the talk position.
In the above hinge assembly, when the abutment members C,D are turned, even if slightly, from the neutral position, the biasing force of the bias means should, theoretically, be converted into a rotational biasing force for returning the abutment members C,D to the neutral position. Actually, however, since the nearby areas (central areas of the projection C1 and the recess D1 in the circumferential direction of the abutment members C,D) of the contact points between the projection C1 and the recess D1 in the neutral position are generally orthogonal to the biasing direction of the bias means, the biasing force of the bias means is hardly converted into the rotational biasing force in the position where the abutment members C,D are slightly turned from the neutral position, and the abutment members C,D are not returned to the neutral position. For this reason, the transmission section A and the reception section B are not positioned in the talk position with a decent degree of modesty. This results in a problem that play is liable to occur.